EE-IS Seminar

Seminar schedule of the Institute for Silicon Photovoltaics: The winter series 2018/19

Seminars take place on Thursdays

at 10:15

in the EE-IS lecture hall: room 227

(Wilhelm-Conrad-Röntgen Campus, Kekuléstr. 5, 1. Floor)

coffee and cookies are available 15 minutes before the seminar.

Please note that are exceptions from this rule, which are highlighted in the seminar plan.


EE-IS seminar announcement

17.01.2019:

Location: seminar room of the PVcomB (Schwarzschildstr. 3, 12489 Berlin)

Harry Mönig (Westfälische Wilhelms-Universität Münster):

The Surface Defect Physics of Chalcopyrite Thin Films: A Combined Scanning Probe Microscopy and Photoelectron Spectroscopy Approach

Abstract

The unusual defect physics of polycrystalline Cu(In,Ga)Se2 (CIGS) thin films is a main issue for a profound understanding of recombination losses in chalcopyrite thin film solar cells. Especially, lateral inhomogeneities and impurity-driven passivation of electronic levels due to structural point defects segregating at the surface and at grain boundaries are extensively debated. In general, defect level spectroscopy experiments provide integral information on a specific sample. Therefore, it is usually challenging to assess if certain spectral signatures originate from the bulk of the material or from a certain spatial region (e.g. an interface, or grain boundary). Here, current imaging tunneling spectroscopy (CITS) can provide valuable information about local variations in the spectral defect density and dipole distribution on semiconductor surfaces with a resolution in the nanometer regime. By combining CITS with photoelectron spectroscopy, the local defect level density and unusual optoelectronic grain boundary properties of different chalcopyrite materials are correlated with the macroscopic energy levels, composition, and dipole formation at the surfaces. Vacuum annealing of different chalcopyrite absorbers provides evidence that sodium diffusion from the glass substrate does not affect the surface defect passivation or grain boundary properties of standard Cu-poor materials. Furthermore, no major impact on the observed heat-induced change in surface band bending (up to 0.6eV) due to sodium could be observed. In contrast, Cu-rich material shows opposing surface defect physics with only minor heat-induced band bending. These results lead to a comprehensive picture, where the highly desirable type inversion at the p/n-interface in standard chalcopyrite thin film solar cells is dominated by band bending within the CIGS absorber, rather than the result of Na impurities or a n-type defect phase segregating at the interface. These results are discussed in view of experimental and theoretical studies suggesting a surface reconstruction as the origin for the Cu-depletion and band gap widening at the surface of chalcopyrite thin films. A basic understanding of the intrinsic surface properties of chalcopyrites will be a fundamental prerequisite to understand the beneficial effect of alkali post-deposition treatments on the solar cell performance.


EE-IS seminar announcement

24.01.2019:

Dr. Sebastian Risse and Dr. Sébastien Cap will speak about

Operando Analysis of Silicon Anodes with Neutrons and Photons

Sebastian Risse1, Arne Ronneburg1,2, Beatrix-Kamelia Seidlhofer1, Marcus Trapp1, Robert Cubitt3, Luca Silvi1, Sébastien Cap4, Bujar Jerliu5, Marcus Trapp1, Erwin Hüger5, Harald Schmidt5,6, André Hilger7, Ingo Manke7, Roland Steitz1, Matthias Ballauff 1,2

  1. Helmholtz-Zentrum Berlin, Institute of Soft Matter and Functional Materials, Berlin, Germany |
  2. Humboldt-University Berlin, Institute of Physics, Berlin, Germany 
  3. Institute Laue Langevin (ILL), Grenoble, France |
  4. Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin, Germany |
  5. Institut für Metallurgie, Technische Universität Clausthal, AG Mikrokinetik, Clausthal-Zellerfeld, Germany |
  6. Clausthaler Zentrum für Materialtechnik, Clausthal-Zellerfeld, Germany |
  7. Helmholtz-Zentrum Berlin, Institute of Applied Materials, Berlin, Germany

Abstract 

Lithiated silicon anodes exhibit a more than ten times higher theoretical specific capacity than current graphite electrodes in Li-ion batteries[1]. Furthermore, silicon is non-hazardous, abundant and its battery operation safety is guaranteed by the suppression of lithium dendrite growth which could cause fatal short circuits.[1] However, Si electrodes exhibit strong capacity fading during electrochemical cycling which has been detrimental for any technical use so far.[1–3] Two major reasons were identified for capacity fading. First, the enormous increase in electrode volume of up to 400% during lithiation and, second, the anew formation/dissolution of a solid electrolyte interface (SEI) during cycling.[4] The complex processes at the Si electrode need measurement methods while the cell is in operation to gain new mechanistic understanding. While operando X-ray imaging yields valuable insights into macroscopic structure formations during volume expansion, operando neutron reflectometry[5,6] is ideally suited for the dynamic process of the several nanometers thick SEI layer. This presentation will give a short introduction to the topic, summarize results from recently published operando neutron reflectometry studies and show some new X-ray imaging results from the BAMline at BESSYII. An outlook at the end will discuss further steps in this field like operando X-ray absorption spectroscopy and the investigation of different layer systems.

[1] X. Zuo, J. Zhu, P. Müller-Buschbaum, Y.-J. Cheng, Nano Energy 2017, 31, 113. | [2] A. L. Michan, G. Divitini, A. J. Pell, M. Leskes, C. Ducati, C. P. Grey, J. Am. Chem. Soc. 2016, 138, 7918. | [3] S. Hansen, E. Quiroga-González, J. Carstensen, H. Föll, Electrochim. Acta 2016, 217, 283. | [4] E. Peled, S. Menkin, J. Electrochem. Soc. 2017, 164, A1703. | [5] B. K. Seidlhofer, B. Jerliu, M. Trapp, E. Hüger, S. Risse, R. Cubitt, H. Schmidt, R. Steitz, M. Ballauff, ACS Nano 2016, 10, 7458. | [6] A. Ronneburg, M. Trapp, R. Cubitt, L. Silvi, S. Cap, M. Ballauff, S. Risse, Energy Storage Mater. 2018, in press.


EE-IS seminar announcement

21th of February:

Dr. Janardan Dagar will speak about

Interface modification via alkali metal salts for both n-i-p and p-i-n perovskite solar cells and modules

Abstract 

Organic–inorganic hybrid perovskite are of great promise, showing a high compatibility with perovskite-based tandem devices and modules. However, transport layer(TL)/perovskite interface defects cause detrimental carrier recombination which are responsible for reduced device performance and high hysteresis. Here, we report Interface modification with alkali salts of N-i-P and P-i-N hybrid perovskite solar cells. The efficient defect passivation significantly suppresses the recombination at the TL/perovskite interface, contributing to enhance the solar cell performance, and the elimination of hysteresis. While measured solar cells with alkali metal (potassium) treatment delivered more than 19% efficiency. We also fabricated perovskite mini-module with the same approach and obtained high performing modules. This approach aims at developing the concept of defect engineering, which can be expanded to multiple-element passivation from monoelement counterparts using simple and low-cost inorganic materials.